Assuming you’re using a spring loaded drag bit: You want to create a tool that’s about .020" in diameter, when you set up depth of cut, set it very, very small, say .001". When you set Z zero, set it on top of the material you’ll use, and be sure to turn OFF the router. I recommend setting it by hand, not using a probe. You may need to adjust the Z down a few thousandths at a time to get a good “drag” - it takes a little trial and error.